P ocedia Enginee ing 190 ( 2017 ) 111 – 117
A ailable online a www.sciencedi ec .com
1877-7058 © 2017 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license
(h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
Pee - e iew unde esponsibili y o he o ganizing commi ee o SPACE 2016
doi: 10.1016/j.p oeng.2017.05.315
ScienceDi ec
S uc u al and Physical Aspec s o Cons uc ion Enginee ing
The Acous ic Emission Pa ame e s Ob ained du ing Th ee-poin
Bending Tes on The mal-s essed Conc e e Specimens
Libo Topolářa,
*
, Ba ba a Kucha czyko áa, Dalibo Kocába, Luboš Pazde aa
aB no Uni e si y o Technology, Facul y o Ci il Enginee ing, Ve eří 331/95, B no 602 00, Czech Republic
Abs ac
Fi e esponse o conc e e s uc u al membe s depends on he mal, mechanical, and de o ma ion p ope ies o conc e e. These
p ope ies a y signi ican ly wi h empe a u e and also depend on he composi ion and cha ac e is ics o he conc e e ba ch mix as
well as hea ing a e and o he en i onmen al condi ions. Conc e e s uc u es could be exposed o ex eme empe a u e condi ions.
Examples o such condi ions a e conc e e ounda ions o launching ocke s ca ying spaceships, conc e e s uc u es in nuclea
powe s a ions o hose acciden ally exposed o i e, o ins ance in he case o unnel i es. This pape analyses acous ic emission
signals cap u ed du ing h ee-poin bending es on he mal-s essed conc e e specimens. The me hod o acous ic emission is an
expe imen al ool sui able o moni o ing he ailu e p ocesses in ma e ials. The ypical pa ame e s o acous ic emission signal
we e iden i ied du ing he acous ic emission eco ds o di e en conc e e specimens o u he desc ibe he unde - he-s ess
beha iou and ailu e de elopmen . The amoun o c ack g ow h was con inuously moni o ed using ou acous ic emission senso s
moun ed on he specimens.
© 2017 The Au ho s. Published by Else ie L d.
Pee - e iew unde esponsibili y o he issue edi o s.
Keywo ds: acous ic emission me hod; h ee-poin bending es ; plain conc e e; high- empe a u e deg ada ion; modulus o elas ici y;
1. In oduc ion
A e he e o is a acks, he wo ldwide in e es in he design o s uc u es o i e g ea ly inc eased. Cu en ly, he
s uc u al i e sa e y is one o he key conside a ions in building applica ions. When subjec ed o hea , conc e e
esponds no jus o ins an aneous physical changes, such as expansion, bu by unde going a ious chemical changes.
* Co esponding au ho . Tel.: +420-541-147-664.
E-mail add ess: opola .l@ ce. u b .cz
© 2017 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license
(h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/).
Pee - e iew unde esponsibili y o he o ganizing commi ee o SPACE 2016
112 Libo Topolář e al. / P ocedia Enginee ing 190 ( 2017 ) 111 – 117
This esponse is especially complex due o he non-uni o mi y o he ma e ial. Conc e e con ains bo h cemen and
agg ega e elemen s, and hese may eac o hea ing in a a ie y o ways. Fi s o all, he e a e a numbe o physical and
chemical changes which occu in he cemen subjec ed o hea [1,2].
Some o hese a e e e sible upon cooling, bu o he s a e non- e e sible and may signi ican ly weaken he conc e e
s uc u e a e a i e. Mos po ous conc e es con ain a ce ain amoun o liquid wa e in hem. This will ob iously
apo ize i he empe a u e signi ican ly exceeds he mois u e le el ange o 100 - 140 °C o so, no mally causing a
build-up o p essu e wi hin he conc e e. I he empe a u e eaches abou 400 °C, he calcium hyd oxide in he cemen
will begin o dehyd a e, gene a ing u he wa e apo and also b inging abou a signi ican educ ion in he physical
s eng h o he ma e ial. O he changes may occu in he agg ega e a highe empe a u es, o example, qua z-based
agg ega es inc ease in olume, due o a mine al ans o ma ion, a abou 575 °C and limes one agg ega es will
decompose a abou 800 °C. In isola ion, he he mal esponse o he agg ega e i sel is mo e s aigh o wa d bu he
o e all esponse o he conc e e due o changes in he agg ega e may be much g ea e . Fo example, di e en ial
expansion be ween he agg ega e and he cemen ma ix may cause c acking and spalling. These physical and chemical
changes in conc e e will ha e he e ec o educing he comp essi e s eng h o he ma e ial. Gene ally, conc e e will
main ain i s comp essi e s eng h un il a c i ical empe a u e is eached, a which poin i will apidly d op o . This
gene ally occu s a a ound 600 °C. This is only a li le highe han c i ical empe a u es o s eel, bu because o he
much lowe conduc i i y o conc e e he hea ends no o pene a e e y a in o he dep h o he ma e ial, meaning
ha he s uc u e as a whole no mally e ains much o i s s eng h ( imbe is simila in being able o e ain s eng h in
i s dep h once su ace laye s ha e been a acked by i e) [3,4].
The dynamic modulus o elas ici y was de e mined by means o wo non-des uc i e me hods. The i s was he
ul asonic (US) pulse eloci y es , which de e mined he dynamic elas ic modulus Ecu. The s a ic modulus o elas ici y
was de e mined by means o he comp essi e es , which is ended by measu ing he specimens’ comp essi e s eng h
(i.e. specimen ailu e).
The p inciple o he ul asonic pulse eloci y es is he epea ed eleasing o ul asonic impulses in o he specimen
and measu ing he ime T equi ed o hem o a el h ough, which is hen used in he de e mina ion o he eloci y
o ul asonic wa e p opaga ion L h ough he conc e e. In he end, he dynamic modulus o elas ici y is calcula ed
using he equa ion:
,10
1
6
2
2
 k
E
Lcu
U
(1)
whe e Ecu is he dynamic modulus o elas ici y in MPa, ρ is he ma e ial’s bulk densi y in kg/m3, L is he ul asonic
pulse eloci y in m/s and k is he dimensionali y coe icien .
The dimensionali y coe icien k equals 1 o a one-dimensional en i onmen , and in he cases o wo- and h ee-
dimensional en i onmen s i depends on he alue o Poisson’s a io μ, which can be de e mined by means o he
esonance me hod (as was done in he expe imen desc ibed he e).
The ime o which he ul asonic pulse a elled h ough each specimen was measu ed longi udinally in h ee
posi ions. The ul asonic wa e eloci y was calcula ed o each posi ion and he a e age o he esul s was used as he
eloci y L in he calcula ion o he elas ic modulus acco ding o (1). The p ocedu e o Ecu de e mina ion was in
acco dance wi h he s anda d [5].
The s a ic modulus o elas ici y o each specimen was de e mined in acco dance wi h he s anda d [6] using 200
mm esis ance s ain gauges and a es ing p ess FORM+TEST ALPHA 3-3000. The esul ing alues o he elas ic
modulus Ec we e calcula ed acco ding o he equa ion:
,
ba
ba
c
E
HH
VV
H
V


'
'
(2)
113
Libo Topolář e al. / P ocedia Enginee ing 190 ( 2017 ) 111 – 117
whe e Ec is he s a ic comp essi e modulus o elas ici y in MPa, σa is he uppe loading s ess in MPa, i.e. 1/3 c, σb is
he basic loading s ess, i.e. 0.5 MPa, εa is he a e age ela i e de o ma ion a uppe loading s ess and εb is he a e age
ela i e de o ma ion a basic loading s ess.
Acous ic emission me hod is a powe ul echnique o non-des uc i e es ing and ma e ials e alua ion. Acous ic
emission (AE) is he e m o he noise emi ed by ma e ials and s uc u es when hey a e subjec ed o s ess. S ess
can be ensile, comp essi e o shea and can ha e componen s in all h ee dimensions. Unde he ac ion o s ess, he
ma e ial expands con ac s o shea s elas ically: his is known as “s ain”. These wa es a el om he sou ce o he
senso s whe e hey a e con e ed o elec ical signals. The AE ins umen a ion measu es hese signals and p oduces
da a displays om which he ope a o e alua es he condi ion and beha iou o he s uc u e unde s ess [7]. This
emission is caused by he apid elease o ene gy wi hin a ma e ial due o e en s such as c ack o ma ion, and he
subsequen ex ension occu ing unde an applied s ess, gene a ing ansien elas ic wa es which can be de ec ed by
piezoelec ic senso s. Acous ic emission me hod can moni o changes in ma e ials beha iou o e a long ime and
wi hou mo ing one o i s componen s i.e. senso s [8,9].
2. Ma e ial and expe imen al se up
Fo expe imen al pa , conc e e samples wi h dimensions o 0.1 x 0.1 x 0.4 m we e p epa ed. Specimens we e
p epa ed acco ding o he ollowing mix design ( o 1m3): 345 kg Po land cemen CEM I (42.5 R Mok á), 848 kg
sand (Žabčice 0/4), 980 kg g a el agg ega e (Olb amo ice 8/16), 2.8 kg supe plas icize (Sika Viscoc e e 2030) and
160 kg wa e in labo a o y o he Ins i u e o Technology o Building Ma e ials and Componen s, Facul y o Ci il
Enginee ing, B no Uni e si y o Technology. Se en se s o es specimens we e manu ac u ed. Each se was labelled
wi h an ID numbe which co esponds o he empe a u e condi ions main ained in he labo a o y u nace du ing i s
hea ing. Specimens labelled 20 ep esen conc e e specimens which d ied eely in labo a o y condi ions wi h
a empe a u e o (21±1) °C and we e no u he hea ed.
The specimens (excep o samples labelled 20) we e imme sed in a wa e ba h o 28 days. Then, hey we e d ied
i s in he labo a o y condi ions and hen in a ce amic u nace a empe a u e 110 °C o ano he 48 hou s. The
conc e e specimens we e hea ed in a p og ammable labo a o y u nace Rhode KE 130B a he hea ing a e o 5 °C/min.
Selec ed empe a u es T= 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C and 1200 °C we e main ained o 60 minu es.
Th ee-poin bending (3PB) es s we e pe o med a e he specimens we e exposed o p esc ibed he mal-s ess
le els. Ten specimens om each se we e es ed. Du ing he es s, an acous ic emission ac i i y was eco ded. Fou
acous ic emission senso s we e a ached o he su ace by beeswax – see in Fig. 1. Acous ic emission signals we e
aken by measu ing de ice DAKEL XEDO wi h ou acous ic emission senso s IDK-09, which included 35 dB
p eampli ie . To elimina e he mechanical and elec ical noise, he gua d senso was used.
The loading es s we e ca ied ou using a Hecke FPZ 100/1 es ing machine a a labo a o y in he Ins i u e o
Building Tes ing, Facul y o Ci il Enginee ing, B no Uni e si y o Technology. Beam specimens wi h ini ial cen al
edge no ches we e loaded unde a 3PB es using he displacemen -con olled me hod which is mo e sui able o
moni o ing he beha iou o specimens a e c ack ini ia ion and du ing i s p opaga ion. The ini ial no ch was made
by a diamond blade saw be o e es ing. The dep h o he no ches was abou 33 mm o all specimens.
114 Libo Topolář e al. / P ocedia Enginee ing 190 ( 2017 ) 111 – 117
Fig. 1. The a angemen o acous ic emission senso s on specimen du ing he h ee-poin bending es .
3. Resul s and discussions
The measu ed alues o selec ed ma e ial p ope ies ob ained om des uc i e and non-des uc i e es s
(comp essi e cube s eng h, s a ic and dynamic modulus o elas ici y) a e summa ized in Table 1. This able also
in oduces in o ma i e changes o bulk densi y alues. I was obse ed ha he conc e e modulus o elas ici y is
signi ican ly a ec ed by he he mal s ess and i s alue dec eases wi h ising empe a u e [9,10]. A high empe a u e,
he disin eg a ion o hyd a ed cemen p oduc s and b eakage o bonds in he mic os uc u e o cemen pas e educe
he elas ic modulus. The ange o educ ion depends on mois u e loss, high- empe a u e c eep, and ype o agg ega e
[11]. The s a ic modulus o elas ici y was non-measu able o specimens bu ned a 1000 °C.
Table 1. The selec ed p ope ies o he mally deg aded conc e e.
Specimens ID
P ope ies
20
200
400
600
800
1000
1200
A e age bulk densi y [kg/m3]
2353
2306
2275
2312
2244
2146
2038
Comp essi e cube s eng h [MPa]
52.50
41.80
30.90
26.00
14.00
3.80
10.80
S a ic modulus o elas ici y Ec [GPa]
32.50
30.70
15.10
7.52
3.62
–
4.39
Dynamic modulus o elas ici y Ecu [GPa]
39.80
36.70
17.80
9.64
2.71
0.94
6.10
To desc ibe acous ic emission signals which a e o med du ing he h ee-poin bending es in he specimens,
he ocus was on he selec ed pa ame e s o hese signals, e.g. numbe o e en s, AE ampli ude and AE ene gy.
Ampli ude is he g ea es measu ed ol age in a wa e o m. This is an impo an pa ame e in AE inspec ion because
i de e mines he de ec abili y o he signal. Signals wi h ampli udes below he minimum h eshold will no be
eco ded. Ano he moni o ed pa ame e , acous ic emission ene gy, is di ec ly p opo ional o he a ea unde he
acous ic emission wa e o m. Resul s o analysis o acous ic emission signals cap u ed du ing h ee-poin bending
es s a e in oduced in Fig. 2, Fig. 3 and Fig. 5 whe e mean alues (ob ained om 10 independen measu emen s) and
s anda d de ia ions (as e o ba s) o in es iga ed pa ame e s a e displayed.
Fig. 2 and Fig. 3 p esen s he dependence o a numbe o AE e en s and ampli ude o AE signals on he he mal
s ess le el. The wa es which eme ge and p opaga e wi hin he sample du ing he h ee-poin bending es , can a ec
he ma e ial elemen oscilla ions. The exposu e o ele a ed empe a u es causes a change o s uc u e, leading o he
change in numbe o AE e en s and ampli udes o AE signals. All specimens, which we e hea ed in he ange o 200
o 800 °C, showed e y simila beha iou . The s uc u al changes did no ha e a signi ican in luence on he alue o
ampli udes o AE signals eco ded om he s a o measu emen up o he ime when he specimens eached hei
ul ima e ensile capaci y, which means ha mic o c acks o med du ing he loading was o he same size in all cases.
The explana ion o his phenomenon can be ound in p ocess o conc e e decomposi ion du ing he he mal s ess
115
Libo Topolář e al. / P ocedia Enginee ing 190 ( 2017 ) 111 – 117
applica ion. Hea ing he conc e e up o 100 °C esul s in he dehyd a ion (con e sion o loosely bound o wa e
chemically bound) and he o ma ion o Calcium-Silica e-Hyd a e (C-S-H) and calcium hyd oxide Ca(OH)2 –
Po landi e occu s. Du ing u he aising o hea ing empe a u e up o 200 °C, dehyd a ion o cemen ing compound
begins which esul s in he elease o physically bound wa e along wi h he concu en decomposi ion o hyd a e. The
i s s age o decomposi ion o C-S-H and decomposi ion o gypsum CaSO4.2H2O culmina es be ween 150 °C and
170 °C. Howe e , a numbe o AE e en s is lowe han in he case o specimen labelled 20 (unhea ed), which indica es
a lowe quan i y o new o med mic o c acks. A a empe a u e abo e 200 °C, he elease o physically bound wa e
occu s. Be ween 250 - 300 °C, he hyd a ed cemen phases a e decomposed. Fu he inc ease o empe a u e abo e
300 °C esul s in decomposi ion o Po landi e [Ca(OH)2 ė CaO + H2O] and he signi ican o ma ion o mic o c acks.
The o ma ion o mic o c acks and Po landi e decomposi ion esul ed in a signi ican inc ease in he amoun o mic o
c acks which a ose be o e he eaching he ul ima e ensile capaci y o he es specimens du ing h ee-poin bending
es .
Fig. 2. The dependence o numbe o AE e en s (le ) and ampli ude o AE signals ( igh ) on he mal s ess le el
( eco d o ul ima e ensile capaci y).
Fig. 3. The dependence o numbe o AE e en s (le ) and ampli ude o AE signals ( igh ) on he mal s ess le el
( eco d a whole o measu emen ).
The dec ease o a numbe o AE e en s and alues o ampli ude o AE signals is caused by qua z phase ansi ion
(in he silica e agg ega e) om iclinic sys em o he hexagonal sys em (β a α 573 °C) a e bu ning up o (a )
600 °C (Fig. 3). This esul ed, oge he wi h he in luence o a di e ence in he mal expansion dis up ion bonds
be ween agg ega e and cemen ing compound, in he c ea ion o a small numbe o mic o c acks du ing 3PB es .
When he bu ning empe a u e is inc eased o 800 °C, he second phase o C-S-H and also o calcium ca bona e
[CaCO3 ė CaO + CO2] decomposi ion occu s. This decomposi ion leads o a dec ease in he numbe and size o
a ising mic o c acks (see Fig. 3). In conjunc ion wi h he o al decomposi ion o he cemen ing compound a he
0
50
100
150
200
250
20 200 400 600 800 1000 1200
Numbe o AE e en s [–]
Tempe a u e o deg ada ion [°C]
0
500
1000
1500
2000
2500
20 200 400 600 800 1000 1200
Ampli ude o AE signals [mV]
Tempe a u e o deg ada ion [°C]
0
2000
4000
6000
8000
10000
20 200 400 600 800 1000 1200
Numbe o AE e en s [–]
Tempe a u e o deg ada ion [°C]
0
500
1000
1500
2000
2500
20 200 400 600 800 1000 1200
Ampli ude o AE signals [mV]
Tempe a u e o deg ada ion [°C]

116 Libo Topolář e al. / P ocedia Enginee ing 190 ( 2017 ) 111 – 117
empe a u e o 1000 °C, he lowes alue o he numbe o AE e en s ( he smalles numbe o a ising mic o c acks)
was eco ded o he specimens labelled 1000.
Fo he specimens which we e exposed o a he mal s ess a a empe a u e o 1200 °C, a la ge numbe and size o
o ming mic o c acks we e eco ded again. This is due o a s uc u al change, accompanied by he c ea ion o new
c ys al phases [Wollas oni e β (CaO.SiO2)], which akes place in he specimen’s s uc u e a empe a u es o abo e
1000 °C. In he pho os (Fig. 4) o selec ed specimens a e isible c acks which we e o med by bu ning.
Fig. 4. The pho o o selec ed specimens a e he h ee-poin bending es .
The alues o AE ene gy (Fig. 5) a e in co ela ion wi h he oughness o he pa icula se o conc e e specimens.
The highes alue o AE ene gy was eco ded o specimens exposed o he empe a u e o 200 °C which may indica e
ha also he oughness o he specimen is high (in compa ison wi h no hea ed specimens labelled 20). This implies
ha s uc u al changes p e en om he c ack g ow h, because mo e ene gy is needed o ac u e. Gene ally speaking,
he ising bu ning empe a u e abo e 200 °C causes a dec ease in he quan i y o AE ene gy eleased du ing he h ee-
poin bending es ha indica es he aising b i leness o he ma e ial. This beha iou o conc e e is changed wi h he
empe a u e o abo e 1000 °C, when he Wollas oni e is c ea ed and he inc ease in conc e e oughness can be
obse ed.
Fig. 5. The dependence o ene gy o AE signals on deg ada ion he mal s ess le el
( eco d a whole o measu emen ).
0
2000
4000
6000
8000
20 200 400 600 800 1000 1200
Ene gy o AE signals 10-5[V·s]
Tempe a u e o deg ada ion [°C]
117
Libo Topolář e al. / P ocedia Enginee ing 190 ( 2017 ) 111 – 117
4. Conclusions
In his wo k, se e al expe imen al es s we e ca ied ou and analysed on he mal-s essed conc e e specimens
loaded up o ailu e a e analysed. Specimens wi h cen al no ch we e subjec ed o he h ee-poin bending es . Du ing
he expe imen s, he AE echnique was used o moni o he p og ess o he specimens’ ailu e. I is ob ious, ha
di e en ypes o c acks gene a e di e en AE signals. These di e ences can be ela ed o he deg ee o damage o
he s uc u e. I can be assumed ha highe alue o ampli ude indica es be e mechanical p ope ies o conc e e which
ha e a be e bond o he ma ix. A small numbe o c acks gene a e a small numbe o e en s be o e he ailu e occu s.
The di e en bu ning empe a u e has a signi ican in luence on moni o ed signal pa ame e s o AE. F om he AE
me hod measu emen , he ollowing conclusions may be d awn:
• The mo e b i le ma e ial, he less AE e en s a e eco ded be o e a isible c ack is c ea ed.
• The inc eased AE ene gy and AE ampli ude eco ded o he specimens exposed o he empe a u e abo e
he 1000 °C is p obably connec ed wi h inc ease in oughness o conc e e specimens a e Wollas oni e was c ea ed.
In summa y, he esul s o he expe imen s pe o med as pa o he esea ch p ojec ocused on he mal-s essed
conc e e can be used o he p edic ion o p ope ies o he mal-s essed cemen ma e ials as well as he speci ic
cha ac e is ics o mic o c acks. The p ope ies o he mic o c acks can be linked o he o e all ac u e beha iou o
he ma e ials.
Acknowledgemen s
This pape has been wo ked ou unde he p ojec GAČR No.16-02261S suppo ed by Czech Science Founda ion
and he p ojec No. LO1408 "AdMaS UP - Ad anced Ma e ials, S uc u es and Technologies", suppo ed by Minis y
o Educa ion, You h and Spo s unde he „Na ional Sus ainabili y P og amme I" and unde he p ojec No. S-16-2967
suppo ed by Facul y o Ci il Enginee ing o B no Uni e si y o Technology.
Re e ences
[1] Z.P. Bazan , M.F. Kaplan, Conc e e a High Tempe a u es, Longman, 1996.
[2] R. Ca el, Fi e p o ec ion in Conc e e Tunnels, in: A. Bea d, R. Ca el (Eds.), Handbook o Tunnel Fi e Sa e y, Thomas Tel o d, London, 2005.
[3] I. Fle che , A. Bo g, N. Hi chien, S. Welch, Pe o mance o Conc e e in Fi e: A Re iew o he S a e o he A , wi h a Case S udy o he Windso
Towe Fi e, in: P oceeding 4 h In e na ional Wo kshop o S uc u es in Fi e, 2006.
[4] M. Tupý, K. So i iadis, I. Kusák, M. Luňák, D. Š e ko á, V. Pe ánek, Exposu e o Mo a s Modi ied wi h Rubbe Agg ega es and Polyme
Admix u es o Acid En i onmen s and Ele a ed Tempe a u e Condi ions, Jou nal o Ma e ials in Ci il Enginee ing, Ame ican Socie y o Ci il
Eng., Uni ed S a es, 2015.
[5] ČSN 73 1371, Nedes uk i ní zkoušení be onu – Ul az uko á impulzo á me oda zkoušení be onu, P ague: Czech S anda ds Ins i u e, (2011),
(in Czech).
[6] ČSN ISO 1920-10 Tes ing o conc e e – Pa 10: De e mina ion o s a ic modulus o elas ici y in comp ession, P ague: Czech S anda ds Ins i u e,
(2016). ( his s anda d is he Czech e sion o he English e sion o he In e na ional ISO 1920-10).
[7] Ch.U. G osse, M. Oh su, Acous ic Emission Tes ing, Sp inge -Ve lag, Be lin, 2008.
[8] L. Topolář, L. Pazde a, P. Cik le, Acous ic Emission Moni o ing du ing S a ic Modulus Elas ici y Tes o Conc e e Specimen, in: Expe imen al
S ess Analysis 51, Applied Mechanics and Ma e ials 486, 2014, pp. 267-272.
[9] A. M. Ne ille, P ope ies o conc e e (5 h edi ion), P en ice Hall, Edinbu g Ga e, 2011.
[10] V. Kodu , P ope ies o Conc e e a Ele a ed Tempe a u es, ISRN Ci il Enginee ing (2014), A icle ID 468510.
[11] M.A. Masoud, M. Solikin, Y. Nu chasanah, Comp esi e S eng hs and Modulus o Elas ici y o S eel Fibe Rein o ced Conc e e unde
Di e en Tempe a u e Condi ions, Diss. Uni e si as Muhammadiyah, Su aka a, 2015.